This invention relates generally to couplers for coupling optical signals.
Couplers couple a signal transmitted through a first waveguide into a second waveguide. Couplers may use fibers or planar waveguides.
In a planar waveguide, the optical paths are formed on a substrate using semiconductor processing techniques. A light path may travel through a so-called optical core formed over the substrate. The core may be covered with an appropriate cladding. The optical signal is transmitted through the core and, in some cases, may extend into the cladding. In fact, typically only about 70 percent of the light actually travels inside the core of a waveguide. The remaining 30 percent propagates in the cladding region outside the core.
With existing couplers, control over the degree of coupling is achieved by controlling the degree of spacing between the waveguides to be coupled. It would also be desirable to control one or more of the coupling ratio, wavelength dependence, and polarization dependence for applications ranging from simple optical filters to complex waveguides filters and polarization controlling elements.